> For the complete documentation index, see [llms.txt](https://gryfn.gitbook.io/gryfn-hardware/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gryfn.gitbook.io/gryfn-hardware/gryfn-precision-tracking-module/maintenance/magnetometer-calibration.md).

# Magnetometer Calibration

## Definition

The INS component of the Applanix APX-15 GNSS-INS sensor utilizes a magnetometer, in addition to other onboard sensors, to aid in heading and attitude determination by measuring the vector component of the Earth’s magnetic field. 

"The MAG is only used for very coarse heading initialization so the absolute accuracy of the MAG heading isn't vital to performance. The main heading alignment comes from the \[dynamic alignment procedure] while in-flight." - Applanix Support

Magnetometer calibrations are performed in-flight in just a few minutes, with no external setup beyond the aircraft and payload required.

## Frequency

1. At least once yearly.
2. If any physical changes are made to the payload/configuration/installation.
3. When the magnetic declination changes more than 10-15 degrees (typically corresponding to several hundred miles of range from last calibration).
   * See map here for more information:

{% embed url="<https://www.ncei.noaa.gov/products/world-magnetic-model>" %}

## Requirements

* The calibration requires for the unit to be rotated at least 3 times clock wise and 3 times counter clock wise around the z-axis.&#x20;
* The calibration algorithm is initiated automatically when the receiver is rotated about the Z‐axis a minimum of 0.6 degrees / second.
* The maximum angular rate cannot exceed 40 degrees / second. It should therefore take at least 9 seconds to complete a full 360 degree rotation about one axis.
* Don’t move further away from power on location than 50m for calibration procedure.

## Instructions

To begin a magnetometer calibration:

1. Turn on the aircraft and power the payload.
   1. Aircraft should be far from buildings, cars, or other metal objects.
2. Let the UAV **sit static for at least 1 minute**.
3. Take off and hover in place at 10-25m AGL.
4. Begin rotating (yawing) the UAV clockwise, completing **each 360 degree rotation in no less than 9 seconds.**
5. Complete **at minimum** 3 rotations clockwise.
6. Repeat rotations counter-clockwise.
7. Land the UAV&#x20;

To check that the calibration was completed properly:

1. Connect an ethernet cable between your laptop and the system's GNSS ethernet port&#x20;
2. Go to IP address 10.0.65.100 in a browser&#x20;
3. If prompted, Username: admin; Password: password&#x20;
4. Receiver Status -> INS Status
5. Ensure the latest calibration date and time match today’s date&#x20;
   1. If the date/time has not updated, power off the system, wait at least 10 minutes, then repeat the calibration.